Ultra-fine fibrous carbon and preparation method thereof

ABSTRACT

The present invention discloses ultra-fine fibrous carbon and preparation of the same. Specifically, the present ultra-fine fibrous carbon is characterized by the graphite-like structure with the sp 2  hybrid carbon content of more than 95% per total content; the (002) plane interlayer spacing (d 002 , d-spacing of C(002) profiles determined by X-ray diffraction method) of 0.3370-0.3700 nm; the (002) plane stacking of more than 4 layers, namely the stacking height (Lc002) of more than 1.5 nm; fibrous carbon length per fibrous carbon width of diameter (aspect ratio) of more than 20; the average diameter of 5˜50 nm.

TECHNICAL FIELD

This invention relates to production of ultra-fine fibrous carbon andpreparation method for the same. Specifically, the present ultra-finefibrous carbon comprises more than 95% carbon atoms, which was designedfor practical applications such as polymer composites, a catalystsupport of fuel cells and organic reaction, a gas storage medium ofhydrogen or methane, a electrode or conductor in lithium secondarybattery and super EDLC (electric double layer capacitor), wherein the(002) plane interlayer spacing (d002, hereinafter) ranges 0.3370˜0.3700nm; the (002) plane stacking consists of more than 4 layers, namely thestacking height (Lc002, hereinafter) is more than 1.5 nm; fibrous carbonlength per fibrous carbon width or diameter (aspect ratio, hereinafter)is more than 20; the average diameter ranged 5˜50 nm; and there is nocontinuous hollow core therein.

BACKGROUND ART

Several patents or papers have been reported on filamentous nano-carbon(carbon nanofiber or graphite nanofiber) and its preparation. Forexamples, Exxon Research and Engineering Co. (USA) disclosed productionof carbon filaments by dissociating a carbon-containing gas such ascarbon monoxide, acetylene, etc. at a temperature to about 800° C. inthe presence of iron monoxide or iron (U.S. Pat. No. 4,565,683). Also,Hyperion Catalytic International Inc. (USA) disclosed the multi-walledcarbon nanotube, which is characterized by a cylindrical shape, a hollowcore, the aspect ratio of more than 5, an ordered outer region ofmultiple, and substantially continuous 8˜15 layers of ordered carbonatoms having an outside diameter between about 10 and 15 nanometerswhich are catalytically grown from a gaseous carbon-containing compound(Japan Patent No. 62-5000943).

Baker and Rodriguez (U.S. Pat. No. 6,099,960; High surface areananofibers, methods of making, methods of using and products containingsame) disclosed preparation of carbon nanofibers with 50˜800 m²/gsurface areas through catalytic pyrolysis of several hydrocarbons overcatalysts such as iron, nickel, and cobalt at 500˜700° C. Boehm (Boehm,Carbon, 11, 583 (1973)), Murayama (H. Murayama and T. Maeda, Nature,245, 791), and Rodriguez (N. M. Rodriguez, J. Mater. Res. 8: 3233(1993)) reported preparation of filamentous nanocarbons or carbonnanofibers through catalytic pyrolysis over alloys of iron, cobalt, andnickel.

Since report on carbon nanotube and its preparation (S. Iijima, Nature,354, 56 (1991)), a number of studies on preparation and application ofcarbon nanofiber or filamentous nanocarbons have been performed in thelast decade. Carbon nanotube is a nano-sized fibrous carbon ofcylindrical shape with a hollow core of more than 0.4 nm, wherein thehexagonal planes align parallel to the fiber axis. Carbon nanotube isclassified as multi-walled carbon nanotube (MWCNT, concentric stackingof multi layers) and single walled carbon nanotube (SWCNT, only onelayer). SWCNT has 0.4˜5 nm diameters, and the outer diameter of MWCNTranges 2.5˜50 nm.

Comparing to the carbon nanotube, filamentous nanocarbons or carbonnanofibers have the carbon hexagonal planes stacking perpendicular tothe fiber axis (columnar or platelet structure, see FIG. 7) and angledto the fiber axis (herring bone or feather structure, see FIG. 8, ref.)Rodriguez, N. M. 1993. J. Mater. Res. 8: 3233). Carbon nanofibers haveno continuous hollow core, differing from carbon nanotube. Such carbonnanofibers have been synthesized by catalytic pyrolysis of hydrocarbonsor carbon monoxide over VIII metals such as Fe, Co, and Ni as maincatalysts.

Carbon nanofibers or filamentous nanocarbons in practical applicationshave attracted attention no more than as a substitute for carbon black,whereas carbon nanotubes, which are characterized by the diameter ofseveral or several tens nanometers, are expected for many applications:for examples, conductive pigments or composites especially withtransparency; the field emission; nano-electronics; hydrogen storage;and biotech-relating applications.

Such a low potential of carbon nanofibers may be originated fromrelatively large diameters of more than 100 nm, actually further 300 nmin many fibrous carbons, for which the transparency to visible light canbe never expected in solvent or composite containing even less than 1 wt% of them; and for which the conductivity in composites is inferior tocarbon blacks due to inferior contact property. Generally, thetransparency to visible light can be attained when the particle size ordiameter is controlled below 100 nm, preferentially 80 nm. Carbonnanofibers so far have a wide distribution of diameters, furthermorethicker average diameters than 100 nm as above-mentioned. Hence, manyadvantages arising from a nano-size such as transparency cannot beexpected, and it is difficult to homogeneously control the properties intheir practical applications.

Although there are many problems relating to carbon nanofiber and itsapplication as aforementioned, carbon nanofibers or filamentousnanocarbons are characterized by the superior productivity, which isseveral or several tens times higher than that of carbon nanotube,depending on preparation methods. Such high yield results in low prices.Also, superior properties of carbon nanofibers have been reported insome applications, especially hydrogen storage: for examples, Baker andRodriguez reported a marvelous result of 40˜63 wt % hydrogen storage(U.S. Pat. No. 6,159,538). Although such a surprising result has beenproved not to be reproducible (USA DOE Report, IEA Task 12: MetalHydride and carbon for Hydrogen Storage 2001, Project No. C-3-Leader:Richard Chahine (Canada), Assessment of Hydrogen Storage on DifferentCarbons), the same report or other papers suggests that carbonnanofibers are capable of hydrogen storage about 2 times more thanactive carbons under 10 MPa (R. Stroebel, et al., J. Power Sources, 84,221(1999)).

Moreover, carbon nanofibers or filamentous nanocarbons produced overnon-supported catalysts are advantageous in terms of prices, as theynever need burdensome and high cost purification.

DISCLOSURE OF THE INVENTION

The present invention was designed to solve the problems of conventionalcarbon nanofibers as described above, and specifically the purpose ofthis invention is to provide a filamentous carbon or fibrous carbon withvery small diameters to be used for various fields such as pigments,inks, films, coating materials, and composites, especially withtransparency.

Further, the present invention purposed to provide a high yieldpreparation of the ultra-fine fibrous carbon to be used as ahigh-efficient material for overall industry, for examples, a gasstorage medium for hydrogen or methane, a catalyst support of fuel cellsand an electrode or conductor of Li secondary battery and super EDLC.

To achieve the aforementioned purposes, this invention discloses theultra-fine fibrous carbon, wherein (1) the fibrous carbon contains morethan 95 wt % carbon; (2) the fibrous carbon diameters range from 3.5 to79.9 nm; (3) the aspect ratio (fiber length per fiber diameter, nodimension) is more than 20, and the carbon hexagonal planes align angledto the fiber axis, where the angle between the hexagonal plane and thefiber axis is 90° or 5˜65°.

Further, the ultra-fine fibrous carbon of the present invention ischaracterized by preparation of the fibrous carbon over carbonblack-supported metal mixture or alloy catalysts, wherein the metalmixtures or alloys involve nickel, nickel-iron and nickel-molybdenum;the carbon black is characterized by less than 100 m²/g BET-surfacearea, 20˜60 nm particle size, and more than 10 wt % oxygen content; thecarbon black-supported catalyst contains 0.1˜60 wt % metal mixture oralloy per carbon black; and the ultra-fine fibrous carbon is prepared byintroducing carbon source at the flow rate of 0.5˜40 sccm (standard ccper minute) per 1 mg catalyst in the furnace for prescribed time, wherethe carbon source involves C2˜C6 hydrocarbons or mixtures of C2˜C6hydrocarbons and hydrogen.

Also, the ultra-fine fibrous carbon of the present invention ischaracterized by preparation of the fibrous carbon over carbonblack-free metal mixture or alloy catalysts, wherein the carbonblack-free catalysts are prepared through preparation of carbonblack-supported metal mixtures or alloys as above-described, removal ofcarbon black from the carbon black-supported metal mixtures or alloys byoxidation at 300˜500° C. in 5˜40 v/v % oxidative gases such as oxygen orcarbon dioxide in inert gases such as nitrogen, argon or helium, andreduction in 1˜3 times in gas mixtures of 5˜40 v/v % hydrogen innitrogen, argon or helium at 400˜500° C. for 1˜48 h.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 illustrate HR-SEM and HR-TEM photographs of the presentultra-fine fibrous carbons produced in Example 1.

FIGS. 3 a, 3 b and 4 illustrate HR-SEM and HR-TEM photographs of thepresent ultra-fine fibrous carbons produced in Example 11.

FIGS. 5, 6 a and 6 b illustrate HR-SEM and HR-TEM photographs of thepresent ultra-fine fibrous carbons produced in Comparative Example 1.

FIG. 7 shows a 2-dimensional structural model of platelet or columnarfilamentous nanocarbons.

FIG. 8 shows a 2-dimensional structural model of herring-bone or featherfilamentous nanocarbons.

BEST MODE FOR CARRYING OUT THE INVENTION

The ultra-fine fibrous carbon and preparation method thereof accordingto the present invention will now be described in detail through generalpreparation process followed by description of the respective examples.

Generally, filamentous nanocarbons are obtained by growing carbon fromdecomposition of gas-phase compounds at high temperatures over metal oralloy catalysts. Hence, synthesis of filamentous nanocarbons comprisestwo steps: catalyst preparation and synthesis over the catalyst. Thecatalyst mainly involves several transition metals such as iron, nickeland cobalt, and their alloys. Synthesis of filamentous nanocarbons isaffected by critical factors such as the kind and partial pressure ofcarbon sources, and the reaction temperature.

High dispersion of active metals or alloys on supports is attained byparticular interaction or ion exchange between metal compounds andoxygen or heteroatoms on the supports. A representative example isdispersion and reduction of iron nitrate or acetate on alumina. Carbonnanofibers produced over alumina-supported catalysts can be practicallyused for applications after removal of alumina of generally more than100 μm sizes from the product, generally by long time treatment withvery strong acids or heat treatment at more than 2800° C. Actually, theremoval of alumina is a very difficult step in real processes.

In this invention, carbon blacks, which are similar in the structure andproperties with filamentous nanocarbons, are used as a catalyst support,especially a carbon black with amorphous coagulum, small primaryparticle size (around 20 nm), and around 15 w % oxygen content.

More particularly, the catalyst for ultra-fine fibrous carbon in thisinvention comprises nickel as a major catalyst which shows a strongactivity to ethylene, propylene, acetylene, etc below 700° C., whereasiron or molybdenum, which are inactive in the above-described condition,are used as secondary metals to disperse nickel particles in the form ofalloys or mixtures.

In catalyst preparation of nickel and iron dispersing uniformly oncarbon black, the aqueous solution of corresponding nitrates or acetatesis impregnated into a particular carbon black of low graphitization andmore than 10% oxygen content, wherein the content of nickel ornickel-iron components ranges 0.1˜60 wt % per carbon black, preferably1˜30 wt %.

Carbon black-supported catalysts as described above are used as twoforms such as (1) carbon black-supported catalysts as-prepared(CB-supported catalysts, hereafter) and (2) carbon black-free catalysts(CB-free catalysts, hereafter) to produce ultra-fine fibrous carbon inthis invention, wherein the CB-free catalysts contain carbon blackcontent of less than 1 wt %.

In preparation of the CB-free catalysts, the carbon black removal fromthe aforementioned CB-supported catalysts such as CB-supported Ni orNi—Fe is performed in air or gas mixtures of inert gases such asnitrogen, argon or helium and oxidative gases such as oxygen and carbondioxide, where the oxidative gas content ranges 5˜40 v/v %, preferably10˜30 v/v %, at 300˜550° C., preferably 450˜500° C., consequently toprovide Ni or Ni—Fe oxide particles containing less than 1 wt % carbonblack, wherein the oxide particles are finer than those by conventionalcoprecipitation.

In use of CB-supported catalysts in this invention, ultra-fine fibrouscarbons are produced as follows: (1) scattering the above-preparedCB-supported catalysts on an alumina or quartz tray; (2) reducing thecatalyst into active one in a conventional furnace under 5˜40 v/v %hydrogen, preferably 8˜30% in inert gases such as nitrogen, argon orhelium at 400˜520° C., preferably 450˜500° C. for 1˜48 h, preferably1.5˜24 h by 1˜3 times, preferably 1˜2 times repeatedly; (3) introducingcarbon source at the flow rate of 0.5˜40 sccm preferably 1˜1 0 sccm per1 mg catalyst in the furnace at prescribed time for prescribed time,wherein the carbon source involves saturated or unsaturated hydrocarbonscontaining 2˜5 carbon atoms, preferably containing 2˜4 carbon atoms,such as ethylene, acetylene and propane or mixtures of aforementionedhydrocarbons and hydrogen, wherein hydrogen partial pressure in thecarbon source ranges suitably 0˜80 v/v %, wherein the reaction conditionis adjusted at 300˜499° C., preferably 350˜490° C. for 2 min˜12 h,preferably 20 min˜4 h.

In use of CB-free catalysts in this invention, ultra-fine fibrouscarbons are produced as follows: (1) scattering the above-preparedCB-free oxides on an alumina or quartz tray; (2) reducing the oxidesinto active catalysts in a conventional furnace under 5˜40 v/v %hydrogen, preferably 8˜30 v/v % in inert gases such as nitrogen, argonor helium at 400˜520° C., preferably 450˜500° C. for 1˜48 h, preferably1.5˜24 h by 1˜3 times, preferably 1˜2 times repeatedly; (3) introducingcarbon source at the flow rate of 0.5˜40 sccm, preferably 1˜10 sccm per1 mg catalyst in the furnace at prescribed time for prescribed time,wherein the carbon source involves saturated or unsaturated hydrocarbonscontaining 2˜5 carbon atoms, preferably containing 2˜4 carbon atoms,such as ethylene, acetylene and propane or mixtures of aforementionedhydrocarbons and hydrogen, wherein hydrogen partial pressure in thecarbon source ranges suitably 0˜80 v/v %, wherein the reaction conditionis adjusted at 300˜499° C., preferably 350˜490° C. for 2 min˜12 h,preferably 20 min˜4 h.

Through hydrogen reduction, metal nitrates or acetates dispersed on CBfurther experience multi-step segregation into very fine catalystparticles on CB, providing ultra-fine fibrous carbons. However, highertemperatures than 520° C. induce aggregation of such fine particles,leading the diameters of fibrous carbons to more than 80 nm. In thisaspect, the present invention was significantly designed to provideultra-fine fibrous carbons of less than 50 nm diameters through (1)dispersing catalyst particles on a suitable CB, and (2) suppressingmaximally the aggregation of fine particles segregated through suitablereduction.

Also, CB-free oxides are finer than the oxides by conventionalcoprecipitation. Hence, suitable segregation during hydrogen reductionmay provide fine active catalysts for production of fibrous carbons. Assimilar as in CB-supported catalysts, higher temperatures than 520° C.induce particle aggregation and consequently thick fiber of more than 80nm diameters. Therefore, the present invention was delicately designedto provide ultra-fine fibrous carbons containing no CB or in a highpurity through (1) preparation of fine catalyst particles by removing CBfrom CB-supported catalysts under a suitable condition, and (2)suppressing maximally the aggregation of fine particles segregatedthrough suitable reduction.

This invention is illustrated in the examples and comparative exampleswhich follow. The examples or comparative examples are set forth to aidin an understanding of the invention but are not intended to, and shouldnot be construed to, limit in any way the invention as set forth in theclaims which follow thereafter. In all examples and comparative exampleswhich follow, the symbol ‘%’ means weight percentage if there are nodescription.

EXAMPLES Example 1

The following materials used in the examples below may be obtained fromcommercial sources: iron nitrate (iron(III) nitrate nonahydrateFe(NO₃)₃.9H₂O=404.00 (99%, Wako), mp 35˜40° C., d 1.684, sol in water,ethanol, acetone), and nickel nitrate (nickel (II) nitrate hexahydrateNi(NO₃)₂.6H₂O=290.79 (98%, Wako), mp 56.7° C., d 2.05, bp 137, sol in0.4 part water, in alcohol, Ni content 20.19% (Nickel Ni=58.71)) may allbe obtained from Wako Co. (Japan). Carbon black (CB, hereinafter) usedin the examples below is a product (No. 3050) from Mitsubishi ChemicalCo., Japan. Detailed properties of CB are shown in Table 1.

CB-supported Fe/Ni mixture or alloy (1/4 w/w) catalyst was prepared asfollows. The mixture of 29.0 g iron nitrate and 5.0 g nickel nitrate wasdissolved in 200 ml distilled water, and then CB (Table 1) 80 g wasadded to the solution, the mixture being stirred for 30 min. The slurrywas dried in a rotary evaporator at 80° C. under 40 torr, providing aCB-supported Fe/Ni (1/4) catalyst (5% metal content per CB).

CB-supported Fe/Ni(1/4) as prepared above (110 mg) was dispersed in aquartz tray (length:width:depth=100:25:15/mm (outer)), and then the traywas placed in the middle of a quartz tube (45 mm inner diameter), whichwas equipped with a conventional furnace. After He flow at ambienttemperature for 30 min, the gas mixture of 100 sccm hydrogen/helium (20%hydrogen partial pressure) was introduced at 480° C. for 2 h, and thenthe reaction was performed under 200 sccm gas flow composed of a 75:25ethylene:hydrogen (v/v) mixture at 480° C. for 2 h, providing 710 mgproduct involving fibrous carbons and CBs.

Table 2 shows d002, Lc(002), and the surface areas of the fibrouscarbons produced in corresponding examples. Graphitization properties ofthe fibrous carbons were analyzed in X-ray diffraction (RigakuGeigerflex II; CuKα, 40 KV, 30 mA, Stepwise Method) at 2θ 5˜90°. Fromthe diffraction, the average (002) plane interlayer spacing (d002,hereinafter) and the average stacking height of (002) planes (Lc(002),hereinafter) were obtained according to the JSPS procedure (Otani Sugio,et al. Carbon Fibers. Nihon Kindaihensyusya; Tokyo, 1983). The surfaceareas of the fibrous carbons were calculated by using the Dubininequation.

The morphology and structure of ultra-fine fibrous carbons producedabove were examined under a high resolution scanning electron microscope(HR-SEM, Jeol, JSM 6403F) and a transmission electron microscope (TEM,Jeol, JEM 100CX) as shown in FIGS. 1 and 2.

The fibrous carbon as prepared above shows a feather structure whereinthe hexagonal planes align angled to the fibrous carbon axis (the angle45˜80°), distinct from carbon nanotube of which the hexagonal planesalign parallel to the fiber axis with a continuous hollow core.

The average diameters or widths of the fibrous carbons were measured byobservation of 320 million magnified images through TEM monitor inrandom selection of 500 fibrous carbons. The average diameter of thefibrous carbon produced above was 22.5 nm, and 75% of fibrous carbonsranged 12˜32 nm diameters. CB which is the catalyst support is a littleobserved under SEM, but hardly under TEM. The aspect ratio of thefibrous carbon produced above was more than 30.

TABLE 1 Properties of carbon black as described in ‘Materials’ BET.Particle Surface Tinting Volatile Blackness Oxygen Size Area StrengthDBF Absorption (cm³/100 g) Content PH of PVC Content (nm) (m²/g) (%)Powder Beads (%) Value Resin (wt %) 30 48 66 — 175 0.5 7.0 0.20 15.2

Examples 2 to 21 below illustrate production of ultra-fine fibrouscarbons under the same or different conditions over the same ordifferent catalysts, and average diameters, d₀₀₂, Lc(002), and surfaceareas of fibrous carbons produced in corresponding Examples orComparative examples are summarized in Tables 2 and 3.

Example 2

Catalyst prepared as in Example 1 (115 mg) was set in the furnace asdescribed in Example 1. After He flow at ambient temperature for 30 min,the gas mixture of 100 sccm hydrogen/helium (20% hydrogen partialpressure) was introduced at 480° C. for 2 h, and then the reaction wasperformed under 200 sccm gas flow composed of a 75:25 ethylene:hydrogen(v/v) mixture at 400° C. for 2 h, providing 465 mg product involvingfibrous carbons and CBs.

The d002, Lc(002), surface areas, and average diameters of fibrouscarbons produced above were measured by the methods described in Example1 (Table 2). The aspect ratio of the fibrous carbon produced above wasmore than 30.

The fibrous carbon as prepared above shows a columnar structure whereinthe hexagonal planes align perpendicular to the fibrous carbon axis,certainly differing from carbon nanotube of which the hexagonal planesalign parallel to the fiber axis with a continuous hollow core.

Example 3 and 4

Catalyst prepared as in Example 1 was set in the furnace as described inExample 1. After He flow at ambient temperature for 30 min, the gasmixture of 100 ml/min hydrogen/helium (20% hydrogen partial pressure)was introduced at 480° C. for 2 h, and then the reaction was performedunder 200 ml/min gas flow composed of a 75:25 ethylene:hydrogen (v/v)mixture at 350° C. for 2 h (Example 3) and at 320° C. for 2 h (Example4), providing 402 mg and 234 mg product, respectively, involving fibrouscarbons and CBs.

The d002, Lc(002), surface areas, and average diameters of fibrouscarbons produced above were measured by the methods described in Example1 (Table 2). The aspect ratio of the fibrous carbon produced above inboth cases was more than 30.

The structure of fibrous carbon produced above was similar as in Example2.

Example 5

To prepare a CB-free catalyst, catalyst as in Example 1 (1080 mg) wasdispersed in a quartz tray (length:width:depth=100:25:15/mm (outer)),and then the tray was placed in the middle of a quartz tube (45 mm innerdiameter), which was equipped with a conventional furnace. CB combustionfrom catalyst as in Example 1 was performed in dry air at 100 sccm flowrate composed of 20 v/v % oxygen and 80 v/v % nitrogen at 480° C. for 2h, providing 115 mg of a Fe/Ni(1/4) oxide containing less than 1.0 wt %CB content.

The average particle size of Fe/Ni(1/4) oxide as prepared above was 8.4nm in TEM observation.

Fe/Ni(1/4) oxide as prepared above (30 mg) was set in the furnace asdescribed in Example 1. After He flow at ambient temperature for 30 min,the gas mixture of 100 sccm hydrogen/helium (20% hydrogen partialpressure) was introduced at 480° C. for 2 h, and then the reaction wasperformed under 200 sccm gas flow composed of a 75:25 ethylene:hydrogen(v/v) mixture at 480° C. for 2 h, providing 3120 mg fibrous carbons freefrom CBs.

The d002, Lc(002), surface areas, and average diameters of fibrouscarbons produced above were measured by the methods described in Example1 (Table 2). The fibrous carbon as prepared above shows a featherstructure wherein the hexagonal planes align angled to the fibrouscarbon axis (the angle 45˜80°), similar as in Example 1 but distinctfrom carbon nanotube as described above. The average diameters offibrous carbons produced above were 25.7 nm, and the aspect ratio of thefibrous carbon produced above was more than 30.

Example 6

Catalyst and reduction condition were the same as in Example 5, but thereaction was performed under 200 ml/min gas flow composed of a 75:25ethylene:hydrogen (v/v) mixture at 300° C. for 2 h, providing 398 mgfibrous carbons free from CBs.

The d002, Lc(002), surface areas, and average diameters of fibrouscarbons produced above were measured by the methods described in Example1 (Table 2). The structure of fibrous carbon produced above was similaras in Example 2. The average diameters of fibrous carbons produced abovewere 15.7 nm, and the aspect ratio of the fibrous carbon produced abovewas more than 30.

Example 7

Catalyst prepared as in Example 5 was set in the furnace as described inExample 1. After He flow at ambient temperature for 30 min, the gasmixture of 100 sccm hydrogen/helium (20% hydrogen partial pressure) wasintroduced at 480° C. for 8 h, and then the reaction was the same as inExample 5, providing 2980 mg fibrous carbons free from CBs.

The d002, Lc(002), surface areas, and average diameters of fibrouscarbons produced above were measured by the methods described in Example1 (Table 2). The structure of fibrous carbon produced above was similaras in Example 5. The aspect ratio of the fibrous carbon produced abovewas more than 30.

Example 8

CB-supported Ni/Mo (4/1 w/w) was prepared from nickel nitrate (nickel(II) nitrate hexahydrate Ni(NO₃)₂.6H₂O=290.79 (98%, Wako), mp 56.7° C.,d 2.05, bp 137, sol in 0.4 part water, in alcohol, Ni content 20.19%)and ammonium molybdate (hexaammonium heptamolybdate tetrahydrate(NH₄)₆Mo₇O24(4H2O=1235.86 (99.0%), sol in water, insol in alcohol)according to the preparation procedure as described in Example 1. Metalcontent was 5% in CB-supported Ni/Mo (4/1).

CB-supported Ni/Mo (4/1) as prepared above (117 mg) was set in thefurnace as described in Example 1. After He flow at ambient temperaturefor 30 min, the gas mixture of 100 sccm hydrogen/helium (20% hydrogenpartial pressure) was introduced at 480° C. for 2 h, and then thereaction was performed under 200 sccm gas flow composed of a 50:50ethylene:hydrogen (v/v) mixture at 480° C. for 2 h, providing 845 mgproduct involving fibrous carbons and CBs.

The d002, Lc(002), surface areas, and average diameters of fibrouscarbons produced above were measured by the methods described in Example1 (Table 2). The fibrous carbon as prepared above shows a featherstructure wherein the hexagonal planes align angled to the fibrouscarbon axis (the angle 45˜80°), but distinct from carbon nanotube asdescribed above. The average diameters of fibrous carbons produced abovewere 40.3 nm, and the aspect ratio of the fibrous carbon produced abovewas more than 30.

Example 9

To prepare a CB-free catalyst, catalyst as in Example 8 (117 mg) was setin the furnace as described in Example 1. CB from catalyst as in Example8 was combusted in dry air at 100 sccm flow rate composed of 20 v/v %oxygen and 80 v/v % nitrogen at 400° C. for 5 h, and successively heliumwas flowed for 30 min before the hydrogen reduction for 1 h at 480° C.in the gas mixture of 100 sccm hydrogen/helium (20% hydrogen partialpressure), providing a CB-free Ni/Mo (4/1) catalyst.

CB-free Ni/Mo (4/1) as prepared above (30 mg) was set in the furnace asdescribed in Example 1. After He flow at ambient temperature for 30 min,the gas mixture of 100 sccm hydrogen/helium (20% hydrogen partialpressure) was introduced at 480° C. for 2 h, and then the reaction wasperformed under 200 sccm gas flow composed of a 50:50 ethylene:hydrogen(v/v) mixture at 480° C. for 2 h, providing 3120 mg fibrous carbons freefrom CBs.

The d002, Lc(002), surface areas, and average diameters of fibrouscarbons produced above were measured by the methods described in Example1 (Table 2). The fibrous carbon as prepared above shows a featherstructure wherein the hexagonal planes align angled to the fibrouscarbon axis (the angle 45˜80°), similar as in Example 5 but distinctfrom carbon nanotube as described above. The average diameters offibrous carbons produced above were 43.1 nm, and the aspect ratio of thefibrous carbon produced above was more than 30.

Example 10

CB-supported Fe/Ni (3/2 w/w) was prepared from iron and nickel nitratesaccording to the preparation procedure as described in Example 1 Metalcontent was 5% in CB-supported Fe/Ni (3/2).

CB-supported Fe/Ni (3/2) as prepared above was set in the furnace asdescribed in Example 1. After He flow at ambient temperature for 30 min,the catalyst was reduced in the gas mixture of 100 sccm hydrogen/helium(10% hydrogen partial pressure) at 480° C. for 20 h. After cooling downto ambient temperature, passivation of the reduced catalyst wasperformed by exposure to 2 v/v % oxygen in helium (flow rate 100 sccm)for 30 min, providing a reduced CB-supported Fe/Ni (3/2).

Reduced CB-supported Fe/Ni (3/2) as prepared above (116 mg) was set inthe furnace as described in Example 1. After He flow at ambienttemperature for 30 min, the gas mixture of 100 sccm hydrogen/helium (20%hydrogen partial pressure) was introduced at 480° C. for 2 h, and thenthe reaction was performed under 200 sccm gas flow composed of a 75:25ethylene:hydrogen (v/v) mixture at 480° C. for 2 h, providing 468 mgproduct involving fibrous carbons and CBs.

The d002, Lc(002), and surface areas of fibrous carbons produced abovewere measured by the methods described in Example 1 (Table 2). Thefibrous carbon as prepared above shows a feather structure wherein thehexagonal planes align angled to the fibrous carbon axis (the angle45˜80°), similar as Examples 1, 5, 8, and 9, but distinct from carbonnanotube as described above. The average diameters or widths of thefibrous carbons were measured by observation of 320 million magnifiedimages through TEM monitor in random selection of 500 fibrous carbons.The average diameter of the fibrous carbon produced above was 33.4 nm,and 75% of fibrous carbons ranged 23˜33 nm diameters. The aspect ratioof the fibrous carbon produced above was more than 30.

TABLE 2 X-ray diffraction properties N₂ BET Average d₀₀₂ Lc(002) surfacearea diameter (nm) (nm) (m²/g) (nm) Example 1 0.3423 2.4 262 22.5Example 2 0.3439 2.2 270 22.4 Example 3 0.3522 1.8 314 15.7 Example 40.3537 1.7 335 12.6 Example 5 0.3543 1.7 390 25.7 Example 6 0.3414 2.6180 15.7 Example 7 0.3430 2.1 244 21.4 Example 8 0.3402 3.2 203 40.3Example 9 0.3405 3.4 231 43.1 Example 10 0.3445 3.2 180 33.4 C-example*1 0.3414 5.2 94 140.3 C-example 2 — — — — C-example 3 0.3456 4.8 140164.4 C-example 4 0.3461 5.6 122 130.8 C-example 5 0.3391 12.2 80.3150.6 *C-example is the abbreviation of ‘Comparative example’.

Example 11

Catalyst as in Example 1 was set in the furnace as described inExample 1. CB from catalyst as in Example 1 was combusted in dry air at100 sccm flow rate composed of 20 v/v % oxygen and 80 v/v % nitrogen at400° C. for 5 h, providing a Fe/Ni(1/4) oxide containing less than 1.0wt % CB content.

After He flow at ambient temperature for 30 min, Fe/Ni (1/4) oxide asprepared above was reduced in the gas mixture of 100 sccmhydrogen/helium (20% hydrogen partial pressure) at 480° C. for 1 h.After cooling down to ambient temperature, passivation was performed byexposure to 2 v/v % oxygen in helium (flow rate 100 sccm) for 30 min,providing a Fe/Ni (1/4) alloy.

Fe/Ni (1/4) alloy as prepared above (30 mg) was set in the furnace asdescribed in Example 1. After He flow at ambient temperature for 30 min,the gas mixture of 100 sccm hydrogen/helium (20% hydrogen partialpressure) was introduced at 480° C. for 2 h, and then the reaction wasperformed under 200 sccm gas flow composed of a 75:25 ethylene:hydrogen(v/v) mixture at 480° C. for 2 h, providing 5224 mg fibrous carbons freefrom CBs.

The d002, Lc(002), surface areas, and average diameters of fibrouscarbons produced above were measured by the methods described in Example1 (Table 3). The structure of fibrous carbon produced above was afeather type as shown in FIGS. 3 a, 3 b and 4.

The average diameters or widths of the fibrous carbons were measured byobservation of 320 million magnified images through TEM monitor inrandom selection of 500 fibrous carbons. The average diameter of thefibrous carbon produced above was 18.2 nm, and 75% of fibrous carbonsranged 8˜28 nm diameters. The aspect ratio of the fibrous carbonproduced above was more than 30.

Example 12

Catalyst prepared as in Example 11 was set in the furnace as describedin Example 1. After He flow at ambient temperature for 30 min, the gasmixture of 100 sccm hydrogen/helium (20% hydrogen partial pressure) wasintroduced at 480° C. for 2 h, and then the reaction was performed under200 sccm gas flow composed of a 75:25 ethylene:hydrogen (v/v) mixture at400° C. for 2 h, providing 1573 mg fibrous carbons free from CBs.

The d002, Lc(002), surface areas, and average diameters of fibrouscarbons produced above were measured by the methods described in Example1 (Table 3). The structure of fibrous carbons produced above was acolumnar type, similar as in Example 2. The average diameters of fibrouscarbons produced above were 10.4 nm, and the aspect ratio of the fibrouscarbon produced above was more than 30.

Example 13 and 14

Catalyst and reaction condition were the same as in Example 11, butreduction was performed under gas mixture of 100 mL/min hydrogen/helium(20% hydrogen partial pressure) at 480° C. for 7 h (Example 13) and for4 h (Example 14), providing 4270 mg and 4380 mg fibrous carbons freefrom CBs, respectively.

The structure of fibrous carbons produced above was a feather type, thesame one as in Example 11. The d002, Lc(002), surface areas, and averagediameters of fibrous carbons produced above were measured by the methodsdescribed in Example 1 (Table 3). The aspect ratio of the fibrous carbonproduced above in both cases was more than 30.

Examples 15, 16 and 17

Catalyst and reduction condition were the same as in Example 12, but thereaction was performed under 200 sccm gas flow composed of a 75:25ethylene:hydrogen (v/v) mixture at 430° C. for 1 h (Example 15), at 390°C. for 1 h (Example 16), and at 350° C. for 2 h (Example 17), providingfibrous carbons of 1350 mg, 1050 mg, and 480 mg, respectively.

The d002, Lc(002), surface areas, and average diameters of fibrouscarbons produced above were measured by the methods described in Example1 (Table 3). The structure of fibrous carbons produced above was acolumnar type, similar as in Example 14. The average diameters offibrous carbons produced above were 20.6 nm (Example 15), 21.7 nm(Example 16) and 14.4 nm (Example 17), respectively, and the aspectratio of the fibrous carbons produced above was more than 30.

Examples 18 and 19

Catalyst, reduction condition, and reaction condition were the same asin Example 11, but the carbon sources were differently a 50:50ethylene:hydrogen (v/v) mixture (Example 18) and a 100:0ethylene:hydrogen (v/v) mixture (Example 19), providing fibrous carbonsof 3620 mg and 1820 mg, respectively.

The d002, Lc(002), surface areas, and average diameters of fibrouscarbons produced above were measured by the methods described in Example1 (Table 3). The structure of fibrous carbons produced above was similaras in Example 17. The average diameters of fibrous carbons producedabove were 13.7 nm (Example 18) and 22.8 nm (Example 19), respectively,and the aspect ratio of the fibrous carbons produced above was more than30.

Example 20

Catalyst, reduction condition and reaction condition were the same as inExample 10, except that reaction temperature was 500° C., providing 3024mg fibrous carbons.

The d002, Lc(002), surface areas, and average diameters of fibrouscarbons produced above were measured by the methods described in Example1 (Table 3). The structure of fibrous carbons produced above was afeather type. The average diameters or widths of the fibrous carbonswere measured by observation of 320 million magnified images through TEMmonitor in random selection of 500 fibrous carbons. The average diameterof the fibrous carbon produced above was 23.4 nm, and 75% of fibrouscarbons ranged 10˜25 nm diameters. The aspect ratio of the fibrouscarbon produced above was more than 30.

Example 21

CB-supported Ni was prepared from nickel nitrate according to thepreparation procedure as described in Example 1. Metal content was 5% inCB-supported Ni.

CB from CB-supported Ni as prepared above was combusted in dry air at100 sccm flow rate composed of 20 v/v % oxygen and 80 v/v % nitrogen at450° C. for 5 h, providing a Ni oxide containing less than 1.0 wt % CBcontent. After He flow at ambient temperature for 30 min, Ni oxide asprepared above was reduced in the gas mixture of 100 sccmhydrogen/helium (20% hydrogen partial pressure) at 480° C. for 1 h.After cooling down to ambient temperature, passivation was performed byexposure to 2 v/v % oxygen in helium (flow rate 100 scam) for 30 min,providing a Ni catalyst free from CBs.

Ni catalyst as prepared above (30 mg) was set in the furnace asdescribed in Example 1. After He flow at ambient temperature for 30 min,the gas mixture of 100 sccm hydrogen/helium (20% hydrogen partialpressure) was introduced at 480° C. for 2 h, and then the reaction wasperformed under 200 scam gas flow composed of a 75:25 ethylene:hydrogen(v/v) mixture at 480° C. for 2 h, providing 320 mg fibrous carbons freefrom CBs.

The d002, Lc(002), surface areas, and average diameters of fibrouscarbons produced above were measured by the methods described in Example1 (Table 3). The fibrous carbons as prepared above shows a featherstructure wherein the hexagonal planes align angled to the fibrouscarbon axis, distinct from carbon nanotube as described above.

The average diameters or widths of the fibrous carbons were measured byobservation of 320 million magnified images through TEM monitor inrandom selection of 500 fibrous carbons. The average diameter of thefibrous carbon produced above was 29.0 nm. The aspect ratio of thefibrous carbon produced above was more than 30.

TABLE 3 X-ray diffraction properties N₂ BET d₀₀₂ Lc (002) surface areaDiameter (nm) (nm) (m²/g) (nm) Example 11 0.3441 4.7 286 18.2 Example 120.3444 4.7 510 10.4 Example 13 0.3446 4.6 580 8.4 Example 14 0.3448 4.4220 17.6 Example 15 0.3463 3.5 266 20.6 Example 16 0.3470 3.2 279 21.7Example 17 0.3477 2.8 391 14.4 Example 18 0.3490 2.2 410 13.7 Example 190.3501 2.3 220 22.8 Example 20 0.3488 3.1 230 23.4 Example 21 0.3520 2.0214 29.0 C-example* 6 0.3551 1.8 141 220.5 C-example 7 0.3512 2.0 139180.7 C-example 8 0.3488 2.2 123 104.5 C-example 9 0.3555 1.6 182 88.9*C-example is the abbreviation of ‘Comparative example’

Ultra-fine fibrous carbons in this invention, which is different fromconventional filamentous nanocarbons or carbon nanofibers, have verysmall diameters of 5˜50 nm simultaneously with a graphitic structure.Therefore, the fibrous carbon of this invention is expected as asuperior material for practical applications such as transparentconductive composites; transparent electromagnetic shields; lithiumsecondary battery, EDLC, and air cells; catalyst supports for fuel cellsor organic reactions; electrification blocks for solar cells; electricdesalination electrodes; gas storage; isotope separator; and removal ofSO_(x) or NO_(x).

Comparative examples below, which describe filamentous nanocarbons orcarbon fibers over catalysts by conventional coprecipitation, maysupport the originality of ultra-fine fibrous carbons in this invention.

Comparative Example 1

Fe/Ni (1/4) alloy catalyst was prepared by dissolving 29.0 g ironnitrate and 5.0 g nickel nitrate in 200 ml distilled water. To thissolution, while rapidly stirred at room temperature, powdered ammoniumbicarbonate was added until a permanent turbidity formed, and then therewas added rapidly ammonium bicarbonate. After stirring for 10 min, theprecipitate settled for 8 h, and then was washed with distilled water bytwo times and then with ethanol by one time. The filtered precipitatewas dried in a vacuum oven at 80° C. for 8 h. The dry precipitate abovewas set in the furnace as described in Example 1, and then was calcinedin dry air at 100 sccm flow rate composed of 20 v/v % oxygen and 80 v/v% nitrogen at 400° C. for 5 h, resulting in Fe/Ni (1/4) oxide. Fe/Ni(1/4) oxide as prepared above was reduced in a hydrogen:helium mixture(20% hydrogen partial pressure) of 100 sccm flow rate at 500° C. for 20h, and then, after cooling to room temperature, was passivated by 5 v/v% oxygen in helium (flow rate 100 sccm) for 30 min, providing a Fe/Ni(1/4) alloy catalyst.

Fe/Ni (1/4) in this comparative example (30 mg) was set in the furnaceas described in Example 1. After He flow at ambient temperature for 30min, the gas mixture of 100 sccm hydrogen/helium (20% hydrogen partialpressure) was introduced at 540° C. for 2 h, and then the reaction wasperformed under 200 sccm gas flow composed of a 75:25 ethylene:hydrogen(v/v) mixture at 540° C. for 2 h, providing 1410 mg fibrous carbons. Thed002, Lc(002), and surface area of fibrous carbons produced above weremeasured by the methods described in Example 1 (Table 2). The morphologyand structure of ultra-fine fibrous carbons produced above were examinedunder a high resolution scanning electron microscope (HR-SEM, Jeol, JSM6403F) and a transmission electron microscope (TEM, Jeol, JEM 100CX) asshown in FIGS. 5, 6 a and 6 b. The fibrous carbons as prepared aboveshow a columnar structure wherein the hexagonal planes alignperpendicular to the fiber axis, distinct from carbon nanotubes whichhave the hexagonal plane alignment parallel to the fiber axis with acontinuous hollow core.

However, the average diameter of the fibrous carbon produced above was140.3 nm, and many fibrous carbons were found to have actually more than300 nm diameters, which is much thicker than ultra-fine fibrous carbonsin this invention.

Comparative Examples 2 and 3

Catalyst as in Comparative example 1 was used, and, after He flow atambient temperature for 30 min, the gas mixture of 100 sccmhydrogen/helium (20% hydrogen partial pressure) was introduced at 480°C. for 2 h, and then the reaction was performed under 200 sccm gas flowcomposed of a 50:50 ethylene:hydrogen (v/v) mixture at 430° C. for 2 h(Comparative example 2) and at 600° C. for 1 h, providing 1620 mg offibrous carbons.

Fibrous carbon produced in Comparative example 3 was examined on thed002, Lc(002), surface area, and average diameter by the methodsdescribed in Example 1 (Table 2). The fibrous carbons as prepared aboveshow a columnar structure wherein the hexagonal planes alignperpendicular to the fiber axis, distinct from carbon nanotubes whichhave the hexagonal plane alignment parallel to the fiber axis. However,the average diameter of the fibrous carbon produced above was 164.4 nm,and many fibrous carbons were found to have actually more than 300 nmdiameters, and the aspect ratio of many fibrous carbons was more than10.

Comparative Example 4

Catalyst, reduction condition and reaction gases were the same as inComparative example 3, except that reaction temperature and time were680° C. and 1 h, providing 330 mg fibrous carbons. During the reaction,a lot of yellowish compounds were adsorbed on inner surface of both endsof the quartz tube, suggesting active thermal decomposition of ethyleneforming amorphous carbons, and the yellowish compounds were proved asrelatively high molecular hydrocarbons by post-analysis.

Fibrous carbon produced above was examined on the d002, Lc(002), surfacearea, and average diameter by the methods described in Example 1 (Table2). The average diameter of the fibrous carbon produced above was 130.8nm, and many fibrous carbons were found to have actually more than 300nm diameters, and the aspect ratio of many fibrous carbons was more than10.

Comparative Example 5

A Fe/Ni (8/2 w/w) alloy catalyst was prepared from iron nitrate, nickelnitrate and ammonium bicarbonate according to the preparation procedureas described in Comparative example 1.

Fe/Ni (8/2) as prepared above (30 mg) was set in the furnace asdescribed in Example 1. After He flow at ambient temperature for 30 min,the gas mixture of 100 sccm hydrogen/helium (20% hydrogen partialpressure) was introduced at 600° C. for 2 h, and then the reaction wasperformed under 200 sccm gas flow composed of a 75:25 CO:hydrogen (v/v)mixture at 600° C. for 2 h, providing 1820 mg fibrous carbons.

The fibrous carbon as prepared above shows a feather structure whereinthe hexagonal planes align angled to the fibrous carbon axis, distinctfrom carbon nanotubes which have the hexagonal plane alignment parallelto the fiber axis. The average diameter of the fibrous carbon producedabove was 150.6 nm, and many fibrous carbons were found to have actuallymore than 300 nm diameters, and the aspect ratio of many fibrous carbonswas more than 10.

The fibrous carbons as prepared above show a columnar structure whereinthe hexagonal planes align perpendicular to the fiber axis, distinctfrom carbon nanotubes which have the hexagonal plane alignment parallelto the fiber axis.

Comparative Example 6

A Fe/Ni (614 w/w) alloy catalyst was prepared from iron nitrate, nickelnitrate and ammonium bicarbonate according to the preparation procedureas described in Comparative example 1.

Fe/Ni (6/4) as prepared above (30 mg) was set in the furnace asdescribed in Example 1. After He flow at ambient temperature for 30 min,the gas mixture of 100 sccm hydrogen/helium (20% hydrogen partialpressure) was introduced at 480° C. for 2 h, and then the reaction wasperformed under 200 sccm gas flow composed of a 50:50 ethylene:hydrogen(v/v) mixture at 600° C. for 1 h, providing 940 mg fibrous carbons.

Fibrous carbon produced above was examined on the d002, Lc(002), surfacearea, and average diameter by the methods described in Example 1 (Table3). The fibrous carbon as prepared above shows a feather structure,similar as in Comparative example 1.

The average diameter of the fibrous carbon produced above was 220.5 nm,and very many fibrous carbons were found to have actually more than 300nm diameters. The aspect ratio was more than 10.

Comparative Example 7

A Ni catalyst was prepared from iron nitrate, and ammonium bicarbonateaccording to the preparation procedure as described in Comparativeexample 1.

Ni catalyst as prepared above (30 mg) was set in the furnace asdescribed in Example 1. After He flow at ambient temperature for 30 min,the gas mixture of 100 sccm hydrogen/helium (20% hydrogen partialpressure) was introduced at 480° C. for 2 h, and then the reaction wasperformed under 200 sccm gas flow composed of a ethylene:hydrogenmixture (50% hydrogen partial pressure) at 600° C. for 1 h, providing940 mg fibrous carbons.

Fibrous carbon produced above was examined on the d002, Lc(002), surfacearea, and average diameter by the methods described in Example 1 (Table3). The fibrous carbon as prepared above shows a feather structure,similar as in Comparative example 1.

The average diameter of the fibrous carbon produced above was 180.7 nm,and fibrous carbons of more than 300 nm diameters were considerablyfound in the product. The aspect ratio was more than 10.

Comparative Example 8

Catalyst as in Example 1 was used, and, after He flow at ambienttemperature for 30 min, the gas mixture of 100 sccm hydrogen/helium (20%hydrogen partial pressure) was introduced at 600° C. for 2 h, and thenthe reaction was performed under 200 sccm gas flow composed of a 75:25ethylene:hydrogen (v/v) mixture at 600° C. for 2 h, providing 2856 mgfibrous carbons.

Fibrous carbon produced above was examined on the d002, Lc(002), surfacearea, and average diameter by the methods described in Example 1 (Table3).

To examine the morphology of fibrous carbons as prepared above, SEM(Jeol, JSM 6403F) was used. The structure of fibrous carbons as preparedabove was of a herring bone type, wherein the hexagonal planes alignangled to the fiber axis (Rodriguez, N. M. 1993. J. Mater. Res. 8:3233), differing from the carbon nanotubes.

The average diameter of the fibrous carbon produced above was 104.5 nm,and more than 60% of fibrous carbons ranged 80˜150 nm diameters. Thinfibrous carbons as prepared above tended to have spiral structure like acoil, and a majority of the fibrous carbons were of the mixture ofbranched one, helical one (modified coil type), and straight fibrouscarbon. The aspect ratio was more than 10.

Comparative Example 9

Silica-supported Fe/Ni mixture or alloy (1/4 w/w) catalyst was preparedas follows. The mixture of 29.0 g iron nitrate and 5.0 g nickel nitratewas dissolved in 200 ml distilled water, and then fumed silica 80 g wasadded to the solution, the mixture being stirred for 30 min. The slurrywas dried in a rotary evaporator at 80° C. under 40 torr, providing asilica-supported Fe/Ni (1/4) catalyst (5% metal content per silica).

Silica-supported Fe/Ni(1/4) as prepared above (110 mg) was dispersed ina quartz tray (length:width:depth=100:25:15/mm (outer)), and then thetray was placed in the middle of a quartz tube (45 mm inner diameter),which was equipped with a conventional furnace. After He flow at ambienttemperature for 30 min, the gas mixture of 100 sccm hydrogen/helium (20%hydrogen partial pressure) was introduced at 600° C. for 2 h, and thenthe reaction was performed under 200 sccm gas flow composed of a 75:25ethylene:hydrogen (v/v) mixture at 600° C. for 2 h, providing 2856 mgfibrous carbons containing silica.

The surface areas of the fibrous carbons were calculated by using theDubinin equation from N₂ isotherm (the BET method), given in Table 3.

The morphology and structure of ultra-fine fibrous carbons producedabove were examined under a high resolution scanning electron microscope(HR-SEM, Jeol, JSM 6403F), and the fibrous carbon as prepared aboveshows a Herringbone structure wherein the hexagonal planes align angledto the fibrous carbon axis (Rodriguez, N. M. J. Mater. Res. 8: 3233(1993)), distinct from carbon nanotube of which the hexagonal planesalign parallel to the fiber axis.

The average diameters or widths of the fibrous carbons were measured byobservation of 320 million magnified images through TEM monitor inrandom selection of 500 fibrous carbons. The average diameter of thefibrous carbon produced above was 88.9 nm, and 60% of fibrous carbonsranged 80˜150 nm diameters. Thin fibrous carbons as prepared abovetended to have spiral structure like a coil, and a majority of thefibrous carbons were of the mixture of branched one, helical one(modified coil type), and straight fibrous carbon. The aspect ratio wasmore than 10.

INDUSTRIAL APPLICABILITY

As described above, the ultra-fine fibrous carbon and preparation methodthereof in the present invention can provide fibrous carbons of 5˜50 nmdiameters with no continuous hollow core which have been known to bevery difficult to achieve. This ultra-fine fibrous carbon can be used asa superior material such as ink additives, film materials, polymercomposites, and electromagnetic shields, especially wherein thetransparency of such products can be attained and controlled byadjusting the addition content of the ultra-fine fibrous carbons.Furthermore, this ultra-fine fibrous carbon can be used as a superiormaterial such as a superior material for a catalyst support of fuelcells and organic reaction, a gas storage medium of hydrogen or methane,and a catalyst or catalyst support for removal of NOx and SOx.

1. A method for producing a fibrous carbon characterized by stacking ofcarbon hexagonal planes having one or double directional growth axis,wherein (1) carbon content is more than 95 wt %; (2) the diameters rangefrom 3.5 to 79.0 nm; (3) the aspect ratio (length per diameter) is morethan 20; and (4) the carbon hexagonal planes align perpendicular to thefiber axis with no continuous hollow core therein, the methodcomprising: using carbon black-supported metal mixture or alloycatalysts, wherein the metal mixtures or alloys comprise nickel as amajor catalyst, and iron or molybdenum as secondary metals; the carbonblack is characterized by less than 100 m²/g BET-surface area, 20-60 nmparticle size, and more than 10 wt % oxygen content; and the carbonblack-supported catalyst contains 0.1-60 wt % metal mixture or alloy percarbon black; and reducing the catalyst 1-3 times in a furnace in gascontaining 5-40 v/v % hydrogen in inert gases such as nitrogen, argon orhelium at 400-500° C. for 1-48 h; and introducing a carbon source into afurnace at the flow rate of 0.5-40 sccm per 1 mg catalyst, where thecarbon source comprises hydrocarbons containing 2-6 carbon atoms ormixtures of aforementioned hydrocarbons and hydrogen.
 2. A methodaccording to claim 1, wherein the mixture of hydrocarbons and hydrogencontains between 0-80 v/v % hydrogen; the production temperature isselected between 300-499° C.; and the production time is selectedbetween 2 min-12 h.
 3. A method according to claim 1, furthercomprising: oxidizing the carbon black-supported catalyst to containless than 1 wt % carbon black at 300-500° C. in oxidative gas containing5-40v/v % oxygen or carbon dioxide in inert gases such as nitrogen,argon or helium.
 4. A method according to claim 3, wherein said alloy iscomposed of 0.1/0.9-0.95/0.05 (wt/wt) of Ni/Fe; 0.05/0.95-0.95/0.05(wt/wt) of Ni/Co; and 0.1/0.9-0.9/0.1 (wt/wt) of Ni/Mo.